Much research and manufacturing today requires precision metrology, very accurate measurement and inspection of mass produced and custom components, components in wind turbines, jet engines, combustion gas turbines, nuclear reactors, ships, automobiles, other aviation components, medical devices and prosthetics, 3D printers, plastics, fiber optics, other optics for telescopes, microscopes, cameras, and so on. The list is long, and the problems are large. In inspecting an airframe, for example, an inspection checks the diameter and circularity of each of thousands of holes at different depths to ensure that each hole is perpendicular to a surface, circular in cross section as opposed to elliptical, not conical, not hourglass-shaped, and so on. Such inspections are performed by human quality assurance inspectors, who inspect large groups of holes at one time, extremely laboriously. When a drill bit or mill head becomes chipped or otherwise damaged, its current hole and all its potentially hundreds or thousands of subsequent holes are out of tolerance, none of which are identified until inspection.
Prior art attempts at high precision measurement include focal microscopy for fringe pattern analysis, that is image analysis by comparison with a pre-image of a correct part, all difficult to deploy and not very accurate. Other prior art includes capacitive probes such as described for example in U.S. 2012/0288336. Such capacitive probes, however, take measurements in only one direction at a time, requiring multiple measurements to assess a part, never assembling a complete image of the inside of a part. Moreover, a capacitive probe must fit tightly into or onto a part to be measured, aligned closely to the center axis of the hole, and for calibration purposes, must have the same probe-to-hole-side separation at all times—because its capacitance is calibrated according to the thickness of the layer of air between the probe and a component to be scanned or measured. When such a capacitive probe identifies a problem with a part, and the part is redrilled or remilled to a larger size, the capacitive probe must be swapped out to a larger diameter probe in order to remeasure the part.
Prior art optical scanners typically are too bulky to move with respect to a part under inspection. Such optical scanners are typically mounted on a fixture with a scanned part in a jig that moves with respect to the scanner. This fixed physical orientation between the optical scanner and a part to be scanned or measured means that there are always aspects of the part that cannot be reached, measured, scanned, or imaged by such a prior art optical scanner. This limitation of prior art has given rise to so-called multi-sensor metrology devices that include both optical scan capability and also tactile sensors that attempt to measure portions of a part that optical scan illumination cannot reach—all in an attempt to build a scanner that can scan a part accurately and completely. One manufacturer of metrology equipment, for example, combines three types of sensor probes, a light section sensor, a shape-from-focus (SFF) sensor, and a tactile sensor, all of which are said to work in unison to achieve optimum measurement, even in areas where scan illumination cannot reach. There continues in the industry some real need for an optical scanner with better reach.